1. Field of the Invention
The present invention relates to a vacuum pump used for a semiconductor manufacturing apparatus, and particularly, to a structure for preventing defect accompanied by a damage of a fastening-bolt that connects the pump and a process chamber, which is caused due to damaging torque.
2. Description of the Related Art
A vacuum pump such as a turbo molecular pump is employed as means for exhausting gas in a chamber in such a step that processes are performed in a process chamber (hereinafter, referred to as xe2x80x9cchamberxe2x80x9d) of high vacuum, such as a dry etching process of semiconductor manufacturing step or a CVD process.
FIG. 5 shows a conventional basic structure of this kind of vacuum pump. A pump case 1 of a vacuum pump shown in FIG. 5 is provided with a gas inlet port 2 at the upper surface and an exhaust pipe that serves as an exhaust port 3 at one side portion of the lower portion, is formed in a cylindrical-shape and is attached to a base 1xe2x80x941.
The bottom portion of the base 1xe2x80x941 is covered with an end plate 4, and a stator column 5 is provided so as to be erected at the center portion of internal bottom surface thereof.
A rotor shaft 7 is rotatably bore through an upper ball bearing 6 and a lower ball bearing 6 at the center of the stator column 5.
A driving motor 8 is arranged inside the stator column 5. The driving motor 8 has a structure in which a stator element 8a is disposed inside the stator column 5 and a rotator element 8b is disposed on the rotor shaft 8, and it is structured such that the rotor shaft 7 is rotated about the shaft.
A rotor 9, which covers the outer circumference of the stator column 5 and is formed in a section-shape, is connected to the upper portion protrusion end from the stator column 5 of the rotor shaft 7.
A plurality of rotor blades 10 and a plurality of stator blades 11, which are processed and formed in a blade-shape, are alternately disposed along the rotation center shaft of the rotor 9 between the upper portion side outer circumferential surface of the rotor 9 and the upper portion side inner wall of the pump case 1.
The rotor blades 10 are integrally processed with the rotor 9, to thereby be integrally provided with the upper portion side outer circumferential surface of the rotor 9. Further, the rotor blades 10 can be integrally rotated with the rotor 9. However, the stator blades 11 are positioned and arranged between the upper stage and the lower stage of the rotor blades 10, 10 through a spacer 11a positioned at the upper portion side inner wall of the pump case 1. Further, the stator blades 11 are attached and fixed to the inner wall side of the pump case 1.
A fixed screw stator 12 is arranged at the position opposing the lower portion side outer circumferential surface of the rotor 9. The screw stator 12 is formed in a cylindrical-shape so that the entire shape thereof surrounds the lower portion side outer circumferential surface of the rotor 9, and integrally attached and fixed to the base 1xe2x80x941. Note that a thread groove is formed inside the screw stator 12, that is, at the surface side opposing the rotor 9.
The vacuum pump shown in FIG. 5 is employed as means for exhausting gas in the chamber 14 as described above. However, in this used state, the vacuum pump shown in FIG. 5 is attached and fixed to the lower surface side opening portion of the chamber 14. In the pump-attached and fixed structure, there is adopted a structure in which a flange 1a that is integrally provided with the peripheral end portion of the upper surface of the pump case 1 hits on the peripheral end of the lower surface side opening portion of the chamber 14, and the flange 1a is fastened on the side of the chamber 14 by a plurality of bolts 15 in this state.
The operation of the above vacuum pump will be described. In the vacuum pump, an auxiliary pump (not shown) connected to the gas exhaust port 3 is operated to cause the inside of the chamber 14 to enter the vacuum state of some degree. Thereafter, the driving motor 8 is operated to rotate the rotor 9 and the rotor blades 10 at high speed integrated with the rotor shaft 7.
Thus, the rotor blade 10 of the uppermost stage rotating at high speed imparts downward momentum to gas molecule entered from the gas inlet port 2. The gas molecule including the downward momentum is guided to the stator blade 11 and sent into the side of the rotor blade 10 of the next lower stage. The above momentum impartment to gas molecule and the sending operation are repeated in a lot of stages. As a result, the gas molecule of the side of the gas inlet port 2 is sequentially moved to the inside of the screw stator 12 of the lower portion side of the rotor 9. The exhausting operation of the gas molecule is a gas molecule exhausting operation, which is caused due to interaction between the rotating rotor blades 10 and the fixed stator blades 11.
The gas molecule, which has reached the screw stator 12 of the lower portion side of the rotor 9 through the above-described gas molecule exhausting operation, is compressed by interaction between the rotating rotor 9 and the thread groove formed inside the screw stator 12, and is moved to the side of the gas exhaust port 3, and then is exhausted to the exterior through the auxiliary pump (not shown) from the gas exhaust port 3.
Incidentally, as structural materials of the rotor 9, the rotor blade 10, and the stator blade 11 or the like, which compose the vacuum pump, light alloy, in particular, aluminum alloy is normally employed in many cases. This is because aluminum alloy is excellent in machining and can be precisely processed without difficulty. However, the hardness of aluminum alloy is relatively low as compared with the other materials and aluminum alloy may cause a damage depending on the operating condition. Further, in a rotation body composed of the rotor 9 and the rotor blades 10, a minute drill hole is bored on the lower portion side outer circumferential surface of the rotor 9, to thereby keep the dynamic balance at the time of high-speed rotation. Consequently, there are tendencies for stress to concentrate on the drill hole, and for the damage of the rotor 9 to occur from the drill hole.
However, the conventional vacuum pump shown in FIG. 5 adopts the pump-attached and fixed structure in which the flange 1a of the pump case 1 is connected to the side of the chamber 14 by the bolt 15, as described above. Therefore, for example, the above damage of the rotor 9 occurs during the high-speed rotation of the rotor 9, to thereby generate a high rotation torque (hereinafter, referred to as xe2x80x9cdamaging torquexe2x80x9d) for rotating the entire pump case 1. Thus, the distortion of the pump case 1 is caused due to the damaging torque and a bolt shaft portion 15a of the bolt 15 fails due to the distortion force as shown in FIG. 6, resulting in causing such a defect that the entire pump together with the pump case 1 is released and dropped from the side of the chamber 14. Also, it takes a lot of time to take out the failed bolt shaft 15a of the bolt 15 from the side of the chamber 14. In the worst case, it is necessary that a new tap is built and a new screw hole is provided at the side of the chamber 14. Therefore, the pump changing operation is performed with difficulty.
The present invention is made for solving the above described problems and an object of the present invention is to provide a vacuum pump in which dropping of the pump and troubles accompanied therewith can be prevented in advance even when an abnormality of the pump occurs only to generate damaging torque, and the changing operation of the pump causing the abnormality can be rapidly performed.
To attain the above described object, according to the present invention, there is provided a vacuum pump comprising: a pump case forming an inlet port at an upper surface; a rotor provided rotatably in the pump case; a rotor blade provided integrally with an outer circumferential surface of the rotor; a stator blade positioned and arranged between the rotor blades or at the outside thereof; and a driving motor for rotating the rotor, characterized in that a step is provided at a peripheral end portion of an upper surface of the pump case to form a flange portion, and further the vacuum pump comprises: an auxiliary ring attached and fit to an upper surface of the flange portion, the surface of which is integrated with the upper surface of the pump case; a bolt insertion hole formed so as to pass through an upper surface and a lower surface of the auxiliary ring; a first bolt insertion hole and a second bolt insertion hole formed so as to pass through the upper surface and the lower surface of the flange portion; an auxiliary ring attaching bolt inserted into the bolt insertion hole of the auxiliary ring, screwed in and fixed to the lower portion opening peripheral end of a chamber positioned at the side opposing the upper surface of the pump case; a pump case supporting bolt inserted into the first bolt insertion hole of the flange portion, screwed in and fixed to the auxiliary ring for supporting the pump case; and a pump case fastening bolt inserted into the second bolt insertion hole of the flange portion, screwed in and fixed to the auxiliary ring for fixing the pump case, and a shaft diameter of which being set small as compared with the auxiliary ring attaching bolt and the pump case supporting bolt.
According to the above structure, in the present invention, when damaging torque is generated, a narrow pump fastening bolt as compared with an auxiliary ring attaching bolt and the pump supporting bolt fails from the relationship with respect to the shaft diameter difference to absorb the shock. Then, a pump connected by a pump supporting bolt rotates to cause bending force and shearing force to act on the pump case supporting bolt. The pump supporting bolt is deformed due to such a force, but prevents a damage thereof, and receive the force. The projecting portion of the auxiliary ring attaching bolt is smaller than that of the pump case supporting bolt, and is tightly fastened. Consequently, the normal state can be maintained and the pump-changing-operation after the pump abnormality occurs can be rapidly performed.
The present invention can adopt a structure in which the pump case is formed in a cylindrical-shape, the first bolt insertion hole is constituted of a long hole, a longitudinal direction of which is the circumferential direction of the pump case, and the pump case supporting bolt is inserted into the long hole and screwed in and fixed to the auxiliary ring, and fastening force thereof is set to be smaller than that of the pump case fastening bolt.
According to the structure, even when the pump case fastening bolt fails, the case supporting bolt moves relatively in the circumferential direction of the pump case and is deformed but is prevented from failing. As a result, even when the all of the pump case fastening bolts are damaged, the pump can be prevented from dropping.
The present invention may adopt a structure in which the pump case supporting bolt is attached to a flange through a plain washer and a spring washer. Therefore, the fastening force becomes adjustable in accordance with the amount of deformation of the spring washer, thereby being capable of relatively moving in the circumferential direction.